Collapse of a vertebral body as a result of external injuries (trauma) or osteoporosis is referred to as a vertebral body compression fracture. In the method that is known for the treatment of this kind of fracture, the collapsed vertebral body is repaired by filling the inside thereof with a filler (such as a bone replacement material) through a vertebral arch using a transpedicular technique.
In this treatment method, a collapsed vertebral body is first returned to a substantially original shape, that is, a collapsed vertebral body is reduced, whereby a cavity (a born defective part) is created therein. A filler such as a bone replacement material is then packed into the cavity to repair the vertebral body, or a filler is packed into the cavity to push a fragile spongy bone aside so that the inside of the collapsed vertebral body is reinforced.
Conventionally, in such a treatment method, the inside of the collapsed vertebral body is filled with a granular bone replacement material by directly packing it from an opening formed in the collapsed vertebral body (see JP-A No. 2003-169811, for example).
However, it is troublesome to fill the inside of the collapsed vertebral body with a large amount of the granules of the bone replacement material each having an irregular shape. Further, in the case where the inside of the collapsed vertebral body is filled with a granular bone replacement material using a cylindrical member, a hollow passage of the cylindrical member is likely to be clogged with the bone replacement material due to its irregular shape, so that there is a case that it is difficult to smoothly perform such a filling operation. Furthermore, in the case where the conventional bone replacement material (comprised of granules having irregular shapes) is used, the granules of the bone replacement material introduced into the cavity of the vertebral body is likely to remain near the vicinity of an opening of the distal end of the cylindrical member, thus it is difficult to fill the cavity with a sufficient amount of the bone replacement material. Furthermore, even when the cavity is filled with a large amount of the bone replacement material, it is difficult to increase the filling ratio sufficiently due to the presence of many gaps among the granules. Moreover, each granule of the granular bone replacement material has an irregular shape as described above, and thus some of the granules are formed with protrusions on their surfaces. Such granules are likely to be broken when a load is applied thereto, so that the volume of the vertebral body is decreased. As a result, it is difficult to keep the result of the operation over a long period of time.
Further, in addition to the above method, there is another method which uses a bone replacement material (bone cement) that has fluidity when it is introduced into a vertebral body but will be hardened in the vertebral body. However, when such a material is used, there is a risk that the material will flow out from the vertebral body to thereby damage adjacent nerves or block blood flow, thus problems still remain in its safeness.